I. Field of the Invention
In particular, the invention relates to a measuring apparatus for cylinders, rolls and similar elements to be measured during the grinding operation, equipped with detection systems of the geometrical and dimensional characteristics (for example roundness, shape, diameter, etc.) and/or structural characteristics (for example, the presence of cracks and work hardening, measurement of the hardness, etc.) and/or surface characteristics (for example roughness, states of surface tension, etc.).
II. Description of Related Art
Grinders of cylinders coming from rolling mills, for the production of strips of metallic material, are large dimensional machines which must guarantee high performances in terms of repeatability and accuracy of the measurements effected in addition to precision in revealing the geometrical shapes obtained.
These characteristics relating to precision, surface quality and repeatability to be guaranteed on a wide range of dimensions (in diameter—up to and over 2 m—and in length—up to and over 10 m), are required in a whole range of sectors in addition to the rolling of flat metallic and non-metallic products, such as the paper and printed paper industry, the constructions of engines and large dimensional hydraulic systems, for example pistons, transmission shafts and elbow shafts for marine engines.
The use of these machines is generally indispensable whenever the large dimensions of elements are associated with sophisticated and restrictive geometrical and surface characteristics as well as structural integrity.
In the iron and steel industry, for example, it is common practice for the reconditioning operations of cylinders from rolling mills to be effected in areas adjacent to the rolling mill itself called “cylinder shapers” or in workshops dedicated to the service of various rolling mills. In these spaces, worn and/or damaged cylinders converge to be subjected to a grinding phase suitable for restoring the ideal conditions necessary for the rolling process.
Even tiny variations in the theoretical profile and roundness of the rolling cylinders cause undulations in the strips, surface marks and traces which reduce the commercial value of tons of steel, with obvious damage to the plant which produces and commercializes them. Furthermore, deviations in the roughness requested cause problems in the subsequent surface protection phases of the strip. Finally, small surface defects (such as, for example cracks, work hardening etc.) jeopardize the structural integrity of the cylinder increasing the risk of accidents (for example catastrophic breakages) causing production blockages and enormous repair expenses, naturally also in addition to the most important aspect linked to the safety of the operators.
In order to optimize the reconditioning procedure of the cylinder, it is necessary to measure and subsequently correct its geometry during the grinding process. At the same time, it is necessary to identify the entity and position of defects in order to effect suitable grinding actions for eliminating them.
The present state of the art defines two alternative solutions for measuring these cylinders:                in the paper industry systems have been developed based on 4 points capable of giving an excellent qualitative response with respect to the determination of the roundness characteristics of the cylinder. This solution, however, has the limitation of being assembled on the wheel-holder trolley and consequently operating in synchronization therewith. This implies that, with respect to the quality of the detection, the geometrical measurements and dimensions are satisfactory but cannot be effected during the grinding cycle whereas the structure and surface faults are subject to sampling. The various dimensions of the grinding wheel and sensors envisage that the measurement coil be of a lesser width than that generated by the grinding wheel, making it impossible for the sensor to cover the whole area to be analyzed. As this is consequently a non-exhaustive measurement, an identification of all the faults is not guaranteed;        in the iron and steel industry, on the contrary, alongside the synchronous “traditional” measurement methods (gauge assembled on board the wheel-holder trolley) but with a geometrical and dimensional analysis effected with two sensors which have the same limitations described above, solutions have been developed based on asynchronous detection methods (independent gauge) which operate on two points to effect geometrical and dimensional measurements (shape, profile, diameter, etc.).        
Regulations (for example ISO 4292) establish that a complete and exhaustive measuring of the roundness must be carried out with two measurements on three points and one on two points and that these determinations must be effected independently of each other. It is therefore evident that the procedure and equipment currently on the market are not capable of providing exhaustive measurements. These apparatuses, on the other hand, are perfectly adequate for determining the structural and surface characteristics, as an asynchronous system adapts the pitch of the coil with the dimension of the sensors.
In the “traditional” cycle (synchronous), three phases are necessary for obtaining an exhaustive analysis of the whole processing area:                passage of the grinding wheel,        geometrical and dimensional and, optionally, structural control,        definition of the new processing parameters.        
These operations must be carried out sequentially increasing the cycle time required.
Furthermore, the fact of operating in different times, induces possible errors due to variations in the configuration of the system as a result of accidental events between the two passages.